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HashIterator.pm
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1.1:
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Mon Sep 15 09:20:39 2003 UTC (20 years, 11 months ago) by
foxr
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CVS tags:
version_1_1_X,
version_1_1_3,
version_1_1_2,
version_1_1_1,
version_1_1_0,
version_1_0_99_3,
version_1_0_99_2,
version_1_0_99_1,
version_1_0_99,
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Module to support object based iteration through a hash. Missed adding this to the
CVS repository on the initial commits associated with loncnew.
1: # Implement iteration over a opaque hash.
2: #
3: # $Id: HashIterator.pm,v 1.1 2003/09/15 09:20:39 foxr Exp $
4: #
5: # Copyright Michigan State University Board of Trustees
6: #
7: # This file is part of the LearningOnline Network with CAPA (LON-CAPA).
8: #
9: # LON-CAPA is free software; you can redistribute it and/or modify
10: # it under the terms of the GNU General Public License as published by
11: # the Free Software Foundation; either version 2 of the License, or
12: # (at your option) any later version.
13: #
14: # LON-CAPA is distributed in the hope that it will be useful,
15: # but WITHOUT ANY WARRANTY; without even the implied warranty of
16: # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
17: # GNU General Public License for more details.
18: #
19: # You should have received a copy of the GNU General Public License
20: # along with LON-CAPA; if not, write to the Free Software
21: # Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
22: #
23: # /home/httpd/html/adm/gpl.txt
24: #
25: # http://www.lon-capa.org/
26: #
27:
28: =pod
29:
30: =head1 HashIterator
31:
32: A hash iterator is an object that alows iteration over a hash in a
33: manner analagous to the way that STL iterators allow iteration over
34: those containers. The HashIterator has the effect of hiding the
35: existence of the hash from the caller and instead presenting an
36: iteratable collection to the caller.
37:
38: The intent is for a hash iterator to be an object returned by another
39: object or class to support iteration over some internal hash
40: maintained by the object. Passing the hash itself back breaks data
41: hiding and protection.
42:
43: =head1 Typical usage:
44:
45: use HashIterator;
46: ...
47:
48: $i = HashIterator::new(\%myhash);
49:
50: ...
51:
52: $i->begin();
53: while(! $i->end()) {
54: $itemref = $i->get();
55: $i->next();
56: }
57:
58:
59: =head1 Member Functions:
60:
61: =cut
62:
63: use strict;
64: package HashIterator;
65:
66: =pod
67:
68: =head2 new(hash)
69:
70: Create a new HashIterator object and return a reference to it. Data
71: members of the HashIterator include:
72:
73: =over 4
74:
75: =item Hash
76:
77: Reference to the hash being iterated over.
78:
79: =item Keylist
80:
81: The set of keys in the underlying hash (an anonymous array ref).
82:
83: =item KeyCount
84:
85: The number of keys in the underlying hash.
86:
87: =item Index
88:
89: Position of the iterator within the keylist/hash table.
90:
91: =back
92:
93: =cut
94:
95: sub new {
96: my $class = shift; # Class name...
97: my $hashref = shift; # Maintain this hash.
98: my @keylist = keys(%$hashref);
99: my $keyref= \@keylist;
100: my $keycount = scalar @keylist;
101:
102:
103: my $self = { Hash => $hashref,
104: Keylist => $keyref,
105: KeyCount => $keycount,
106: Index => 0};
107: bless($self, $class); # Type ourself...
108:
109: return $self;
110:
111: }
112:
113: =pod
114:
115: =head2 begin
116:
117: Reset the iterator to the start of iteration.
118:
119: =cut
120:
121: sub begin {
122: my $self = shift; # Get object...
123: $self->{Index} = 0;
124:
125: }
126:
127: =pod
128:
129: =head2 end
130:
131: Return true if the iterator is off the end of the hash.
132:
133: =cut
134:
135: sub end {
136: my $self = shift; # Retrieve self as object.
137: return ($self->{Index} >= $self->{KeyCount});
138: }
139:
140: =pod
141:
142: =head2 get
143:
144: Return the contents of the hash at the current key. If the key is off
145: the end of the hash, undef is returned. What is returned is a copy of
146: the element. If the index is off the end of the iteration, undef is
147: returned.
148:
149: =cut
150:
151: sub get {
152: my $self = shift;
153: if ($self->end()) {
154: return undef;
155: }
156: my $hashref = $self->{Hash};
157: my $key = $self->{Keylist}->[$self->{Index}];
158: return $$hashref{$key};
159: }
160:
161: =pod
162:
163: =head2 next
164:
165: Advances the iterator.
166:
167: =cut
168:
169: sub next {
170: my $self = shift; # Get us.
171: $self->{Index} = $self->{Index} + 1;
172: }
173:
174: 1;
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